The provision of a solid state switch across a pair of separable contacts to reduce arcing between the contacts, when separated, is disclosed within U.S. patent application Ser. No. 610,947 filed May 16, 1984 entitled "Solid State Current Limiting Interrupter" in the name of E. K. Howell and now abandoned. This application is incorporated herein for purposes of reference and should be reviewed for a good description of the circuit components used within the solid state switch.
The absence of an arc between the contacts, when separated, allows smaller contacts which in turn are more readily separated in the early stages of the current waveform to further reduce contact heating and deterioration. U.S. patent application Ser. No. 684,307 filed Dec. 20, 1984 entitled "High Speed Contact Driver For Circuit Interrupter Device" now abandoned and U.S. Pat. No. 4,620,122, entitled "Piezoelectric Contact Driver For Circuit Interrupters", both in the name of E. K. Howell, disclose contact drivers for rapid circuit interruption by means of a pair of fixed contacts and a bridging contact operated by a contact driver. Both of the applications are also incorporated herein for purposes of reference. The use of the solid state switch in combination with the high speed contact driver to separate the contacts allows the solid state circuit components to be reduced in rating and hence more economically feasible. U.S. Pat. No. 4,607,148 entitled "Change Of State Contact Material For Electric Circuit Interrupters", also in the name of E. K. Howell, describes a contact structure that allows for a reduction in the contact holding force which is required to provide low contact resistance between the contacts. This results in the use of smaller contacts and contact holding springs. This application is incorporated herein for purposes of reference and should be reviewed for a good understanding of the materials and arrangement used to promote these benefits.
By the synergistic combination of a solid state switch, high speed contact driver and change of state electrode materials, the size of the contacts and the means for separating the contacts can be reduced sufficiently to enable containment within an evacuated envelope. The use of the evacuated envelope now allows either the fixed contact pair or the bridging contact to be fabricated from copper metal rather than silver. The copper provides good electrical conduction between the contacts along with a substantial reduction in materials costs. The copper remains oxide-free under the vacuum contained within the sealed envelope as well as when reducing-type gases are employed instead of vacuum.